Boron‐Double‐Ring Sheet,Fullerene, and Nanotubes: Potential Hydrogen Storage Materials

Similar to carbon‐based graphene, fullerenes and carbon nanotubes, boron atoms can form sheets, fullerenes, and nanotubes. Here we investigate several of these novel boron structures all based on the boron double ring within the framework of density functional theory. The boron sheet is found to be metallic and flat in its ground state. The spherical boron cage containing 180 atoms is also stable and has I symmetry. Stable nanotubes are obtained by rolling up the boron sheet, and all are metallic. The hydrogen storage capacity of boron nanostructures is also explored, and it is found that Li‐decorated boron sheets and nanotubes are potential candidates for hydrogen storage. For Li‐decorated boron sheets, each Li atom can adsorb a maximum of 4 H₂ molecules with g_d=7.892 wt %. The hydrogen gravimetric density increases to g_d=12.309 wt % for the Li‐decorated (0,6) boron nanotube.     

A New Class of Boron Nanotube

The configurations, stability and electronic structures of a new class of boron sheet and related boron nanotubes are predicted within the framework of density functional theory. This boron sheet is sparser than those of recent proposals. Our theoretic results show that the stable boron sheet remains flat and is metallic. There are bands similar to the π‐bands in graphite near the Fermi level. Stable nanotubes with various diameters and chiral vectors can be rolled from the sheet. Within our study, only the thin (8, 0) nanotube with a band gap of 0.44 eV is semiconducting, while all the other thicker boron nanotubes are metallic, independent of their chirality. It indicates the possibility, in the design of nanodevices, to control the electronic transport properties of the boron nanotube through the diameter.     

碳化硼纳米线的制备和结构

以碳纳米管为模板，通过加热碳纳米管与硼粉的混合物，获得了笔直的硼碳纳米线.对纳米线的结构和成分进行研究，结果表明纳米线主要为B4C纳米线.在部分B4C纳米线的端部存在Ni颗粒，这些端部具有Ni颗粒的纳米线构成了纳米磁针.讨论了B4C纳米线的生长机制，B4C纳米线的生长主要为硼原子在碳纳米管中扩散并发生化学反应，使得碳纳米管晶格结构发生重组，形成B4C纳米线.反应后，硼原子部分取代了碳纳米管中碳原子，修补了碳纳米管中的晶格缺陷，获得了形态笔直的B4C纳米线.     

Dispersible Shortened Boron Nitride Nanotubes with Improved Molecule‐Loading Capacity

The oxidation process of boron nitride nanotubes was thoroughly investigated, and a slow oxidation characteristic was clearly revealed. Subsequently, the controllable oxidation process was utilized to break the sturdy structure of the boron nitride nanotubes to fabricate shortened nanotubes. The shortened boronnitride nanotubes were found to possess good solubility in water and many organic solvents. Further experiments demonstrated remarkably improved molecule‐loading capacity of the shortened boron nitride nanotubes. These dispersible shortened boron nitride nanotubes might have the potential to be developed as effective delivery systems for various molecules, which may find applications in bio‐related fields.     

碳化硼成分分析标准物质的研制

介绍碳化硼成分分析标准物质的制备方法。以硼酸和蔗糖为原材料,酯化反应得到硼酸酯沉淀,经过烧结制备碳化硼粉体。用低温前驱体裂解法制备碳化硼成分分析标准物质,并进行了均匀性检验、稳定性考察,采用8家实验室协作定值,对定值结果的不确定度进行了评定。结果表明,研制的碳化硼成分分析标准物质具有良好的均匀性和稳定性,量值准确可靠,定值结果的相对扩展不确定度为0.003 1%~0.13%(k=2)。     

碳化硅和碳化硼在电催化中的应用

燃料电池是具有广泛应用前景的新能源技术。碳载铂基催化剂（Pt/C）是最常用的燃料电池电极催化剂,不过Pt/C稳定性较差、且成本高昂,严重限制了燃料电池的规模化应用。共价型碳化物碳化硅和碳化硼,由于具有极强的共价键,其物化稳定性优异,成为制备高稳定性、低成本的燃料电池催化剂的重要基础材料。本文总结了相关研究成果,介绍了碳化硅和碳化硼的独特优势,讨论了相关研究的发展方向。     

碳化硅和碳化硼在电催化中的应用

燃料电池是具有广泛应用前景的新能源技术。碳载铂基催化剂(Pt/C)是最常用的燃料电池电极催化剂,不过Pt/C稳定性较差、且成本高昂,严重限制了燃料电池的规模化应用。共价型碳化物碳化硅和碳化硼,由于具有极强的共价键,其物化稳定性优异,成为制备高稳定性、低成本的燃料电池催化剂的重要基础材料。本文总结了相关研究成果,介绍了碳化硅和碳化硼的独特优势,讨论了相关研究的发展方向。     

Boron nanotubes.

A survey of novel classes of nanotubular materials based on boron is presented. Pure boron nanotubes are a consequence of a general Aufbau principle for boron clusters and solid boron phases, which postulates various novel boron materials besides the well-known bulk phases of boron based on boron icosahedra. Furthermore, several numerical studies suggest the existence of a large family of compound nanotubular materials derived from crystalline AlB2. We compare these novel boron-based nanotubular materials to standard nanotubular systems built from carbon, and point out a number of remarkable structural and electronic properties that make boron-based nanotubular materials an ideal component for composite nanodevices and extended nanotubular networks.     

毛刺状竹节结构氮化硼纳米管的合成与生长机理

以非晶硼和氧化镍纳米颗粒为原料,在氨气中1100℃下合成了毛刺状竹节结构的氮化硼纳米管. 利用X射线衍射和透射电镜研究了氮化硼纳米管的结构和形貌. 竹节结构纳米管表面的毛刺是六方氮化硼的纳米薄片. 提出了一种基于固态硼和气态二氧化硼扩散的毛刺形貌生长机理.     

氮化硼纳米管的研究进展

本文较全面地综述了氮化硼(BN)纳米管研究的最新进展,详细讨论了BN纳米管的合成、结构、表征、形成机理及应用等方面的研究现状,并对今后的研究方向进行了展望。     

Hollow boron nitride (BN) nanocages and BN-nanocage-encapsulated nanocrystals

Hollow boron nitride (BN) nanocages (nanospheres, image on the left) and BN-nanocage-encapsulated GaN nanocrystals (right) have been synthesized by using a homemade B-N-O precursors. The as-prepared BN hollow nanocages have typically spherical morphologies with diameters ranging from 30 to 200 nm. The nanocages have crystalline structures. Peanutlike nanocages with double walls have also been observed; their internal space is divided into seperated compartments by the internal walls. The method is extended to sheathe nanocrystals with BN nanocages; BN-shell/GaN-core nanostructures have been successfully fabriacted. The method may be generally applicable to the fabrication BN-sheathed nanocrystals.     

Energetic stability of boron nitride nanostructures doped with one carbon atom

We have investigated, using first‐principles calculations, the role of a substitutional carbon atom on the geometric stability of boron nitride monolayers, nanotubes, and nanocones. It is shown that the formation of energy depends on the number of atoms for the monolayers and on the diameter for the tubes. It is also found, for the carbon‐doped boron nitride nanotubes, that the value for the strain energy approaches the one obtained for nondoped tubes with increasing diameter. For the structural stability, we have verified that the doping, which introduces an excess of nitrogen or boron, makes each structure more favorable in its reverse atmosphere, i.e., excess of nitrogen is more stable in a boron‐rich growth environment, whereas excess of boron is preferred in a nitrogen‐rich condition. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

氮化硼诱导聚乙烯分子结晶的分子动力学模拟

采用分子动力学方法(MD)研究熔体条件下聚乙烯分子在氮化硼纳米管表面和氮化硼片层表面的结晶机理。通过对聚乙烯分子结晶过程中晶体构象的演变、空间内分子分布的变化以及分子扩散特性的研究,从微观角度比较了两种结构氮化硼纳米材料对聚乙烯结晶的影响。结果表明一维结构的氮化硼纳米管诱导聚乙烯结晶的能力远高于二维片层状的氮化硼,说明纳米材料的维度影响着高分子材料的结晶性能。     

纳米结构储氢材料的计算研究与设计

对B原子掺杂的石墨烯、碳纳米管和富勒烯、MB2纳米管和ca表面覆盖的纳米管体系的氢气吸附和存储性能进行了第一原理计算,结果表明在表面曲率比较大的碳材料体系中掺B可以增强其对H2的吸附作用;过渡金属原子与H2由于Kubas作用而表现出很大的H2吸附能;碱土金属Ca离子化后的带电电荷的材料体系,由于与H2发生极化作用,也会增强氢气的吸附性能．综合我们的结果和储氢材料研究的最新进展,讨论了影响储氢材料性能的相关因素,就如何增强材料与H2之间的相互作用,使H2吸附能在0．2～0．4eV之间,能够在温和的条件下吸／放氢,并且具有较大的重量和体积储氢量等问题作了简要论述,这些原理对纳米结构储氢材料的设计有一定的指导意义．     

石墨基底对碳/碳化硼复合纳米绳形成的影响

利用邻碳硼烷(C₂H₁₂B₁₀)作为反应原料,二茂铁(C₁₀H₁₀Fe)作为催化剂,通过化学气相沉积法在石墨基片上生长出一种新颖的碳化硼纳米绳。用X射线衍射仪分析纳米绳的相结构,用场发射扫描电子显微镜(FESEM)和高分辨透射电子显微镜(HRTEM)观察纳米绳的微观形貌和结构,结果发现纳米绳的中心部分是碳化硼纳米线,在线的表面有非晶碳绳结,故纳米绳为碳/碳化硼复合物。研究了绳状产物的生长机理,表明石墨基片对产物的形成有至关重要的作用。     

Nanostructures in Physical Materials Chemistry: An Exploratory Laboratory

The blend of nanotechnology and material science is often beyond the scope of undergraduate laboratories. Through undergraduate research, graphite-intercalated compounds have been incorporated in the production of carbon-based nanostructures. Based on this work a series of exploratory exercises were designed for the undergraduate physical chemistry laboratory emphasizing nanostructure material science. This rapidly expanding area of science and technology can be introduced at an undergraduate level using a high temperature oven to produce nanostructure samples that are analyzed by Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy at research university laboratories, infrared spectroscopy, and a bomb calorimeter. In these experiments we use samples of pure graphite, fluorinated graphite, and lanthanum oxide to induce the formation of nanostructures. An overview of fullerenes, nanotubes, boron nitride and Si nanostructures, other carbon forms, graphite-intercalated compounds, and the storage of hydrogen in nanotubes are provided in an appendix. Several extensions of the laboratory are proposed.     

Thin boron nitride nanotubes with unusual large inner diameters

BN nanotubes, displaying the characteristics of few concentric layers (2–6 layers) but unusual large inner diameters (ranging from 8 to more than 10 nm), are synthesized by a chemical vapor deposition (CVD) method on -Al₂O₃ micrometer-range particles. The inner diameters are at least 5 nm larger than the previously reported BN nanotubes of similar layers. Some BN nanotubes are observed to be filled with B–N–O-based amorphous materials. Crystalline core fillings (in the form of boron carbide nanorods) were also discovered. The discussions suggested that the CVD growth behavior of BN nanotubes may be closely dependent on the underlying substrates, which may be helpful to the possible rational synthesis of BN nanotubes.     

DNA‐Mediated Assembly of Boron Nitride Nanotubes

The dispersion of nanomaterials in solutions is of primary importance for the improvement of their processability, but it also provides a way to investigate phase behavior and to assemble nanostructures in solvents. Several methods based on different interactions have been developed to disperse carbon nanotubes, whereas little development has been made for their boron nitride nanotube (BNNT) counterparts. A direct way to obtain long‐range ordering may be through spontaneous nematic ordering in solutions at sufficiently high concentrations of the nanomaterial fraction. Lyotropic nematics have been observed in various organic and inorganic systems. In this work, the strong interactions between DNA and BNNTs were exploited to fabricate high‐concentration BNNTs aqueous solutions by a simple method, and then, for the first time, nematic ordered ensembles of BNNTs were obtained by filtration. It is proposed that a localized liquid‐crystal phase appears during filtration, as the ordering trend for the BNNTs was found to depend on the concentration of the aqueous solutions of the BNNTs. Moreover, BNNTs were successfully localized on a predefined area by using a thiol‐modified DNA–BNNT hybrid.     

X-ray absorption near edge structure study of BN nanotubes and nanothorns

Two boron nitride (BN) nanostructures, the bamboo-like nanotubes and nanothorns where the nanosize h-BN layers are randomly stacked looking like thorns, were synthesized selectively via thermal chemical vapor deposition of B/B(2)O(3) under the NH(3) flow at 1200 degrees C. Electron energy-loss spectroscopy reveals the N-rich h-BN layers with a ratio of B/N = 0.75-0.85. Angle-resolved X-ray absorption near edge structure of these two N-rich nanostructures has been compared with that of h-BN microcrystals. The pi transition in the N K-edge shifts to the lower energy by 0.8-1.0 eV from that of h-BN microcrystals, and the second-order signals of N 1s electrons become significant. We suggest that the N enrichment would decrease the band gap of nanostructures from that of h-BN microcrystals. The Raman spectrum shows the peak broadening due to the defects of N-rich h-BN layers.